It took some times to weed out all bad stuff and compile this Manga Studio free alternative list. Paint Tool SAI is great free tool also few other applications there. I haven't tested all of these either.

Awe Gimp. How I do not know how to work thou. But Inkscape my love you are as beautiful as a withering rose who life that'll respawn in a bud of a seed. And Pencil oh how I love you so. Let us make many memories togehter <3.

I use to use Photoshop but eventually decided that while it's a good program and a good Idea to have as a graphic design student, I just couldn't afford it on my computer. So for now I use GIMP on my computer. I might switch back to Photoshop though if I can't get all my school projects done in the schools computer lab.